1. Field of the Invention
The present invention relates to radio oscillating and radar systems.
2. Related Art Statement
In Intelligent Transport Systems (ITS), it has been widely demanded a radar system utilizing radio wave such as an on-vehicle radar system. It has recently been developed, and partly commercialized, a radar system utilizing radio wave of 76 GHz band.
An on-vehicle radar system is provided on the front side of a vehicle body so that it can measure the direction, distance and relative velocity of the car with respect to one running ahead of the car to function as a sensor for preventing the car accident. It will be strongly demanded an auto cruise system (ACC) controlling the speed of a vehicle and assuring the safety distance between cars. It is thus required to detect obstacles on the sides such as passing vehicles and a human for the lane selection and those on the back for the assistance of the parking and the prevention of the car accident, as well as obstacles ahead of the car. It has been thus increasingly demanded to fix many radars on the vehicle body.
As shown in FIG. 1, a prior millimeter-wave radar system has an FM modulator, a local oscillator, a power amplifier and multiplier, an electric divider, a transmitting antenna, a receiving antenna and a mixer. Although the RF parts are composed of MMIC, the high cost is a problem to be solved for the wide acceptance. Although it is demanded to equip a plurality of radar systems as described above, such equipment would be very difficult in a practical view because the cost of the RF parts are high as described above.
It is further necessary to reduce the distance of transmission as possible on the viewpoint of losses between the oscillator and divider and between the transmitting antenna and mixer. Since the oscillator is thus provided near the antenna, the oscillator is required to have high reliability under severe circumstances. On the other hand, it is strongly demanded to have stability of frequency, low noise intensity and low phase noise as a radar system. Both of the above demanded properties are needed to be satisfied, so as to increase the cost of the oscillator.
Japanese Patent publication No. 2002-162465A disclosed a radar system utilizing a sub-carrier light source using a mode locking laser. According to the system, incident light can be divided into a plurality of routes by means of an optical fiber and an optical divider. It is thus possible to perform multi-oscillation using a single oscillator and to considerably reduce the number of parts necessary for the RF units, so that the cost can be reduced. It is further possible to freely select the positions of oscillators, so as to relax the requirements for the oscillators and to further reduce the costs.